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<title>Problem 1648. -- [Usaco2006 Dec]Cow Picnic -- 衡阳八中OJ离线版-2012-02-29</title><center><h2>1648: [Usaco2006 Dec]Cow Picnic</h2><span class=green>Time Limit: </span>5 Sec&nbsp;&nbsp;<span class=green>Memory Limit: </span>64 MB<br><span class=green>Submit: </span>162&nbsp;&nbsp;<span class=green>Solved: </span>114<br>[<a href='submitpage.php?id=1648'>Submit</a>][<a href='problemstatus.php?id=1648'>Status</a>][<a href='bbs.php?id=1648'>Discuss</a>]</center><h2>Description</h2><div class=content>The cows are having a picnic! Each of Farmer John's K (1 <= K <=
100) cows is grazing in one of N (1 <= N <= 1,000) pastures,
conveniently numbered 1...N. The pastures are connected by M (1 <=
M <= 10,000) one-way paths (no path connects a pasture to itself).

The cows want to gather in the same pasture for their picnic, but
(because of the one-way paths) some cows may only be able to get
to some pastures. Help the cows out by figuring out how many pastures
are reachable by all cows, and hence are possible picnic locations.

</div><h2>Input</h2><div class=content>* Line 1: Three space-separated integers, respectively: K, N, and M

* Lines 2..K+1: Line i+1 contains a single integer (1..N) which is the
        number of the pasture in which cow i is grazing.

* Lines K+2..M+K+1: Each line contains two space-separated integers,
        respectively A and B (both 1..N and A != B), representing a
        one-way path from pasture A to pasture B.

有一个n个点，m条边的有向图，还有k只奶牛。每个奶牛在一个点上，现在FJ想知道，有多少个点是这k个奶牛都可以到达的。</div><h2>Output</h2><div class=content>* Line 1: The single integer that is the number of pastures that are
        reachable by all cows via the one-way paths.

</div><h2>Sample Input</h2>
			<div class=content><span class=sampledata>2 4 4<br />
2<br />
3<br />
1 2<br />
1 4<br />
2 3<br />
3 4<br />
<br />
<br />
INPUT DETAILS:<br />
<br />
4<--3<br />
^   ^<br />
|   |<br />
|   |<br />
1-->2<br />
<br />
The pastures are laid out as shown above, with cows in pastures 2 and 3.<br />
</span></div><h2>Sample Output</h2>
			<div class=content><span class=sampledata>2<br />
<br />
OUTPUT DETAILS:<br />
<br />
The cows can meet in pastures 3 or 4.<br />
</span></div><h2>HINT</h2>
			<div class=content><p></p></div><h2>Source</h2>
			<div class=content><p><a href='problemset.html?search=Silver'>Silver</a></p></div><center>[<a href='submitpage.php?id=1648'>Submit</a>][<a href='problemstatus.php?id=1648'>Status</a>][<a href='bbs.php?id=1648'>Discuss</a>]</center>﻿<br>

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